The invention relates generally to electronic displays that are addressable by a central computer or host, and relates more specifically to such systems as employ RF communications where battery life is of great concern.
Numerous experimenters have attempted to implement systems for the electronic display of prices in stores. The general concept is old and yet has not until recently been commercially viable due to numerous recent advances in the system design. That the general concept is quite old may be seen, for example, in U.S. Pat. No. 4,002,886 to Sundelin, U.S. Pat. No. 4,500,880 to Gomersall and U.S. Pat. No. 5,198,644 to Pfieffer, all of which show electronic price displays which are in communication with a central computer and which change their displayed information based on messages sent by the central computer. None of those prior art systems has, however, been commercially successful.
In one commercially viable electronic shelf label (ESL) system there are typically 15,000 or more individually addressable labels. These ESLs are situated in areas according to the organization of the store.
Specifically, the ESLs are along a shelf edge, and in some systems are mounted on a rail. Normally several shelves are associated vertically in a vertical bay. Several vertical bays may be logically associated as a section or category, and several sections may be positioned in a half-aisle. Appl. Ser. No. 07/757,260 to Failing et. al. (now U.S. Pat. No. 5,241,467), U.S. Pat. No. 5,172,314 to Poland et al., and U.S. Pat. No. 5,245,534 to Waterhouse et. al., all assigned to the same assignee as the present invention and incorporated herein by reference, describe means and methods to collect, maintain, and use location information on each ESL and the product it represents. This information is then used to cause all ESLs in an area or sub-area to change their displays in response to a user request initiated by a hand held unit, a special purpose module, an initiator, or a display function switch. (The user request may be initiated by any of several means including those set forth in copending U.S. Appl. Ser. No. 07/757,675 for System for Recognizing Display Devices, issued Oct. 21, 1995 as U.S. Pat. No. 5,461,561, and incorporated herein by reference.) In the current art, multiple messages must be prepared and sent, one each to each ESL in the desired area, to effect the desired display change. In a dense area, such as Health And Beauty Aids (HABA), the time necessary to address all the ESLs in a section or several adjacent vertical bays may take several tens of seconds, which is too long to allow for efficient in-aisle inter-activity with ESL-displayed store maintenance information, such as Computer-Aided Ordering (CAO), shelf or space management, inventory management, or promotional or merchandising information. In addition, for a power-limited system, such as an RF or IR system powered by solar cells or batteries, it is desirable to minimize the number of transmissions from each ESL and, more importantly, to minimize the receiver-on time in order to conserve power and extend battery life.
Global commands may be used to cause an entire set of ESLs to respond at once to the same message. With a system that has the capability to track the geographic location of ESLs (and their related products), whether determined by the system itself such as with appending locator modules or by a separate RF means, or whether simply tracked by manual audit means and maintained in the host computer data base, it is desirable to cause ESLs within a selected geographic region to display different information. Current systems may issue global commands, such as to one gondola controller, and command an entire half-aisle to respond to a command. Alternatively, each individual ESL in an area may be individually addressed, a process that might be acceptable in lightly populated or small areas. However, when the number of ESLs in the selected area is large (on the order of 100 to 200 ESLs), the update time may take 10 to 20 seconds. The estimate of 10 to 20 seconds assumes a typical processor clock rate, but it should be appreciated that the update time is a direct tradeoff with the processor clock rate, which in turn is directly related to the power consumption. In a wired system, as mentioned above, power consumption is not necessarily of grave concern. But in a wireless system (at least one using CMOS processors) it is desirable to reduce power consumption and thus to run the processors as slowly as possible; thus limits the bandwidth of the communications channel since the processor's ability to frame incoming serial data of a given baud rate is limited by its clock speed.
Numerous desirable system capabilities are possible only if the labels are in a receiver-on state most of the time. Such capabilities are described, for example, in copending U.S. Appl. Ser. No. 08/201,470, issued on Sep. 5, 1995 as U.S. Pat. No. 5,448,226, entitled Shelf Talker Management System, incorporated herein by reference.
Copending U.S. Appl. Ser. No. 08/247,334, entitled Subglobal Area Addressing for Electronic Price Displays, attempts to address this issue by providing means by which groups of labels may be quickly activated while minimizing the total number of labels required to have receivers on. This solution provides some benefit in trading off response time of a limited geographic area with battery life, but requires some additional software overhead to implement.
As previously mentioned, the receiver-on time is a major factor in the battery life for the electronic price display labels. If global addressing is to be performed, all labels must be "listening" (i.e. in a receiver-on state) if the global query is to be successful. Yet if all labels are in a receiver-on state for a substantial portion of the time, then power consumption increases drastically and battery life drops drastically.
In an RF-linked electronic price display system, it is thus highly desirable to have a way in which the receiver-on time can be as much time as desired, without the drawback of drastically worsened battery life.